Integrated circuitry is utilized in an ever-increasing number of applications. To meet the needs of the expanding applications, new methods of packaging integrated circuits and connecting integrated circuits with other substrates or circuitry have been developed. Various factors must be considered when connecting integrated circuitry with an adjoining substrate or circuit. Such factors include reliability, performance or speed, and size requirements to meet the requirements of higher definition sub-micron integrated circuits.
Conventional circuit interconnections include flip chip bonding, tape automated bonding (TAB) and conventional wire bonding. Flip chip bonding is preferred in rapid communication or high performance applications because shorter signal paths are provided. The pads are provided upon one surface of the flip chip and the pads can be aligned with conductive pads on an opposing substrate for interconnection. Solder or some type of adhesive is typically used to couple the flip chip with the substrate.
Anisotropic conductive adhesives (ACA) including anisotropic conductive film (ACF) and anisotropic conductive paste (ACP) are used for fine pitch interconnections. These interconnections are utilized in exemplary applications including liquid crystal display (LCD) panels, tape carrier packages (TCP), printed circuit board (PCB) interconnections, indium tin oxide (ITO) connections, and flexible circuit substrate connections.
Such anisotropic conductive adhesives typically comprise an adhesive matrix and plural conductive particles within the adhesive matrix. The conductivity of the anisotropic conductive adhesive is determined by the weight percentage of the conductive fillers or number of conductive particles per unit area. The conductive particles are randomly distributed throughout the adhesive matrix in conventional anisotropic conductive adhesives.
Referring to FIG. 1, plural substrates 1, 2 are shown having respective opposing bond pads 3, 4. An anisotropic conductive adhesive 5 is applied intermediate substrates 1, 2. Anisotropic conductive adhesive 5 includes plural conductive particles 6. One conductive particle 6 intermediate bond pads 3, 4 provides electrical coupling of bond pads 3, 4.
Benefits of anisotropic conductive adhesives include the ability to provide electrical conduction in a z-axis or a vertical direction (i.e., intermediate bond pads 3, 4) while providing substantial electrical insulation in horizontal directions (i.e., insulate adjacent bond pads of the substrate). High definition technologies require additional conductive particles (i.e., higher density of anisotropic conductive adhesives) to properly electrically connect all interconnections and bond pads of the devices being connected. Current density passing through the interconnection can be defined by the loading or density of particles in a given volume of the adhesive film and by the surface area of the interface coupling the contacts. Increasing the number of conductive particles results in increased current density.
However, increasing the number of conductive particles within the adhesive films also enhances the chances that the anisotropic conductive adhesive will be conductive in at least one horizontal direction. Such horizontal conduction can lead to short circuits and improper circuit performance.
Therefore, there exists a need to provide interconnections for fine pitch or high definition components without the drawbacks associated with the prior art devices and methodologies.